Project Summary - Project 3 Metastatic progression of prostate cancer to the bone is not curable. Interestingly, the detailed study of paired prostatic tissues from treatment-nave patients who present with bone metastatic disease at diagnosis revealed that the prostatic epithelia of the primary tissue express proteins that are commonly found in cells that reside in the vascular sinusoids and endostea of the bone marrow. More specifically, the primary tumor cells of patients with bone metastasis seemed to mimic megakaryocytes and osteoblasts - to be termed MO-mimicry. We further found that transgenic mice with a loss of TGF-beta receptor type II expression in the prostatic fibroblasts support the MO-mimicry phenotype and can support the expansion of adjacent epithelia in the bone microenvironment. The microdissection of stromal cells around the cancer epithelia expressing MO-mimicry features revealed the juxtacrine signaling pathways involving Notch signaling and associated transcription factors that were epigenetically up regulated. Thus, by stromal-epithelial interactions in the primary prostate tumor mimicking bone marrow cells it may enable the tumor cells to survive in the bone niche. If true, this suggests that primary tumor foci may hold the risk determinants for bone colonization. It would be a leap in clinical diagnosis capability if prostate biopsy tissue could diagnose or predict the otherwise undetectable bone metastatic disease. In this highly collaborative proposal we hope to provide the biologic and clinical evidence to address the hypothesis, primary tumor microenvironment facilitates epithelial acquisition of MO-mimicry features that enable colonization of bone. In Aim 1 we will define the role of carcinoma associated fibroblasts in inducing and/or supporting MO-mimicry. These studies will involve the interrogation of the heterogeneous fibroblasts that support Notch-signaling mediated expansion of PC epithelia in bone. In Aim 2 we will evaluate interactions of MO-mimicry PC epithelia at the vascular and endosteal niche on bone engraftment. We will determine if blocking the marrow vascular niche where megakaryocytes reside affect bone dissemination and endosteal colonization. Finally, in Aim 3 we will determine if detection of the MO-mimicry profile in diagnostic prostate biopsies is an indicator of clinical bone metastases and/or occult bone metastasis.